Recently, there are an increasing number of vehicles loaded with a plurality of image processing devices such as a navigation system, a DTV, a DVD player, a car-mounted camera. Therefore, when communications are established for a car-mounted image processing device and so on, a light multichannel transfer system having a small number of wires and harnesses is demanded.
For example, a camera 11 depicted as FIG. 1 fetches an image of a place falling on a blind spot of the view of a driver such as the side of a road, the backward of a vehicle, and outputs the image to a main display 15 and a rear-seat display 17 connected to the main display 15 via a bus 16. A DVD player 12 regenerates a DVD. A terrestrial wave digital broadcast tuner 13 selects terrestrial waves and converts them into video signals, converts the video signals into digital image data, and outputs them to the main display 15 and the rear-seat display 17. A car navigation system 14 updates the information indicating the current position of a car at predetermined intervals, and outputs the information to the main display 15 and the rear-seat display 17.
Thus, when a plurality of video sources are transferred from each image processing device, they are routed among plural image processing devices using harnesses and wires as described above. Therefore, it is necessary to transmit them in a simpler configuration with the number of wires and harnesses decreased.
According to the patent document 1, image processing devices such as a car-mounted camera are provided, and the power source to the image processing devices is supplied from a battery via a power supply line by cable. However, signals (data) are transmitted and received by wireless, not by cable. The signals transmitted and received between the camera control device for performing image processing and the image processing device can be captured video signals, control signals and so on. The video signals are processed and the video is displayed on a display.
Thus, proposed is a car-mounted camera system capable of receiving multichannel signals for eliminating the harnesses to realize a light system, reducing the cost of a cable and an assembly cost, and stably transmitting video signals in real time by connecting the car-mounted camera to the camera control device by wireless.
The patent document 2 discloses compressing and transmitting video to transmit the video using a transmission line of a narrow band (about 10 Mbps). A first transmission/reception device and a second transmission/reception device are provided for each of an instrument panel unit and a trunk room to mutually multiplex information signals of car-mounted electronic equipment, and a control signal for communications of an information signal between the first transmission/reception device and the second transmission/reception device is unified with an information signal. With the above-mentioned configuration, proposed are a communication device and a vehicle loaded with the communication device capable of easily performing communications by unifying an information signal of electronic equipment and a control signal of the information signal between a first transmission/reception device and a second transmission/reception device provided for each of an instrument panel unit and a trunk room to mutually multiplex information signals of connected electronic equipment.
The patent document 3 proposes omitting the trouble of converting data of a program stream output from an MPEG (moving picture experts group) 2 encoder into an MPEG 2 transport stream by dividing the data of the program stream output from the MPEG 2 encoder in a data transmission device, generating a packet by adding a header to the divided pack, and transmitting the packet using an IEEE (Institute of Electrical and Electronics Engineers) 1394 interface.
The patent document 4 proposes a car-mounted multichannel image processing device capable of easily processing multichannel image information about the vicinity of a vehicle. That is, scanning an image at equal intervals and in a predetermined order, or scanning an image at intervals and in an order changed depending on the operation state is proposed.
However, in the operation environment depicted as FIG. 1, the image data to be transmitted by each image processing device dynamically changes. Therefore, the image data of plural pieces of video transmitted from plural image processing devices cannot be efficiently transmitted.
In the image encoding and transmitting system using a low cost compressing system with the conventional car-mounted camera, data is compressed at a predetermined bit rate depending on the image size and the frame rate, and the number of channels to be transferred is statically determined by the bandwidth in the transmission line.
That is, when a plurality of channels are used in a conventional method, the number of channels is increased on the basis of a predetermined bit rate, and if a bandwidth of a transmission line is exceeded, the number cannot be increased any more.
The patent documents 1 through 4 do not disclose realizing a dynamic transmission of data through a plurality of channels as high quality images in a system of transmitting data in a fixed length by compressing the data after converting an image into a variable length code collectively in a plurality of lines. That is, they do not disclose determining a compression rate dynamically depending on the number of channels for transmitting image data by determining a compression rate for image data from each channel (so that the upper limit of the execution bandwidth can be approached, and the high quality image (low compression) can be read), and determining a fixed size in which data is transmitted to one frame depending on the determined compression rate.                Patent Document 1: Japanese Laid-open Patent Publication No. 2005-117614        Patent Document 2: Japanese Laid-open Patent Publication No. 2000-151643        Patent Document 3: Japanese Laid-open Patent Publication No. 11-177581        Patent Document 4: Japanese Laid-open Patent Publication No. 10-260324        